1. Field of the Invention
The present invention relates to a current limiting circuit for controlled semiconductor power components, in particular to a current limiting circuit for power transistors.
Integrated power circuits require effective protection against current overloading at their outputs, in order to prevent thermal destruction in the event of a possible short circuit.
While the invention is applicable in principle to all controlled semiconductor power components, the present invention and the problem area on which it is based are explained with reference to power ICs using hybrid technology which provide not only MOS power transistors but also bipolar components and CMOS components.
The customary basic principle for such a current limiting circuit consists in the total current flowing through the power transistor or, using the sense cell principle, part of this total current generating a voltage drop across a resistor (also referred to as shunt resistor).
If the voltage drop exceeds a predetermined maximum value, the current limiting circuit loads the drive signal of the power transistor to such a great extent that the output current of the power transistor, which can be determined from the drive signal by way of the family of output characteristic curves, remains below a permissible limit value.
There exist a variety of approaches in the prior art for implementing that basic principle in circuitry terms.
In general, a distinction is made between current-regulation limiting circuits and voltage-regulation limiting circuits.
Current-regulation limiting circuits generally require a filter for masking inrush spikes. Voltage-regulation limiting circuits require temperature compensation circuits. Furthermore, the prior art circuits of both circuit types again themselves require complex protective circuitry for the occurrence of a short circuit.
Examples of that prior art are found in xe2x80x9cSmart Power ICs: Technologies and Applications,xe2x80x9d Murari, Bertotti, and Vignola (Eds.), pp. 328, 400, 426, Springer Verlag, Berlin-Heidelberg-New York, 1996.
U.S. Pat. No. 5,519,341 to Corsi et al. discribes a current limiting circuit for a power transistor with a current sense resistor and a comparator comprising four bipolar transistors and two current sources. The current threshold at which the comparator responds can be set by way of the emitter areas of the cross-connected bipolar transistors.
A further current limiter circuit is disclosed in German patent DE 44 29 716. There, a current mirror circuit is connected to the current sense resistor.
It is accordingly an object of the invention to provide a current limiting circuit, which overcomes the above-mentioned disadvantages of the heretofore-known devices of this general type and which can be realized in a simple manner, functions largely independently of its voltage supply and has a high accuracy.
With the foregoing and other objects in view there is provided, in accordance with the invention, a current limiting circuit for a controlled semiconductor power component having a main current path, a source terminal, and a control terminal, the circuit which comprises:
a sense resistor connected in series with a main current path of a controlled semiconductor power component, the sense resistor having a terminal connected to a source terminal of the semiconductor power component;
a first supply voltage terminal and a second supply voltage terminal;
a first bipolar transistor having a collector, an emitter, a base, and load path, a second bipolar transistor having a collector, a base, and a load path, and a current source connected in series with the load paths between the first supply voltage terminal and the terminal of the sense resistor connected to the source terminal of the semiconductor power component, the first bipolar transistor and the second bipolar transistors being connected such that respective collector currents thereof are proportional to one another;
a third bipolar transistor having an emitter and a load path, and a fourth bipolar transistor having a base, a collector, and a load path connected in series with the load path of the third bipolar transistor between the control terminal and the second supply voltage terminal, the emitter of the third bipolar transistor receiving a current impressed on the emitter proportional to a collector current of the fourth bipolar transistor;
the collector and the base of the first bipolar transistor being connected to the base of the third bipolar transistor;
the base of the second bipolar transistor being coupled to a node between the emitter of the third bipolar transistor and the collector of the fourth bipolar transistor;
the base of the fourth bipolar transistor being coupled to a node between the emitter of the first bipolar transistor and the collector of the second bipolar transistor;
whereby an emitter-to-base voltage of the fourth bipolar transistor contains, as voltage components, a voltage drop across the sense resistor, an emitter-to-base voltage of the second and third bipolar transistors with positive sign, and an emitter-to-base voltage of the first bipolar transistor with negative sign, and further voltage components resulting from differences between emitter-to-base voltages of further bipolar transistors operated with a different emitter current density; and
wherein the bipolar transistors are of the same type.
With the above and other objects in view there is also provided, in accordance with the invention, a current limiting circuit for a controlled semiconductor power component driven with a drive potential and having a main current path, comprising:
a current sense resistor connected in series with a main current path of a controlled semiconductor power component;
a load output terminal;
a first current mirror including a first PNP bipolar transistor having a collector and having an emitter connected to a drive potential of a semiconductor power component, and a second PNP bipolar transistor having an emitter connected to the drive potential of the semiconductor power component;
a second current mirror including a third PNP bipolar transistor having an emitter connected to the drive potential of the semiconductor power component, and a fourth PNP bipolar transistor having an emitter connected to the drive potential of the semiconductor power component;
a third current mirror including a first MOS transistor having a source connected to reference ground potential, and a second MOS transistor having a drain and a source connected to the reference-ground potential;
a fourth current mirror including a third MOS transistor having a drain and having a source connected to the reference ground potential and a fourth MOS transistor having a collector and a source connected to the reference ground potential;
a first NPN bipolar transistor having a base, a collector, and an emitter connected to the drain of the third MOS transistor;
a second NPN bipolar transistor connected between the collector of the fourth PNP bipolar transistor and a terminal of the sense resistor connected to the semiconductor power component, the second NPN bipolar transistor having a base;
a third NPN bipolar transistor having a base connected to the base of the first NPN bipolar transistor, a collector, and an emitter connected to the drain of the second MOS transistor and to the base of the second NPN bipolar transistor;
a fourth NPN bipolar transistor connected between the collector of the first PNP bipolar transistor and the terminal of the sense resistor connected to the load output terminal, the fourth NPN bipolar transistor having a base connected to of the emitter of the first NPN bipolar transistor;
a diode connecting the collectors of the first and the third NPN bipolar transistors to the drive potential of the semiconductor power component in the forward direction;
a fifth MOS transistor and a sixth MOS transistor connected in series between the reference-ground potential of the fourth current mirror and a terminal of the semiconductor power component connected to a supply potential;
the fifth MOS transistor having a gate connected to the collector of the third PNP bipolar transistor and the sixth MOS transistor having a gate connected to the drive potential of the semiconductor power component; and
the base of the first NPN bipolar transistor and the base of the third NPN bipolar transistor being commonly connected to a node between the fifth MOS transistor and the sixth MOS transistors.
In other words, the objects of the invention are satisfied by way of a current limiting circuit for controlled semiconductor power components, in particular for power transistors, with a sense resistor which is connected in series with the main current path of the controlled semiconductor power component, for the purpose of generating a voltage drop reproducing the current through the controlled semiconductor power component.
The second embodiment is particularly suitable for high-side switches.
In accordance with an added feature of the invention, at least one of the four bipolar transistors has an emitter area which differs from that of the other bipolar transistors.
In accordance with an additional feature of the invention, the current limiting circuit has the following further features:
a fifth and a sixth bipolar transistor, which are connected, in each case in series with an associated current source, between the first and second reference-ground potentials;
where the base of the second bipolar transistor is connected to a node located between the emitter of the fifth bipolar transistor and the corresponding current source, and the base of the fifth bipolar transistor is connected to a node located between the emitter of the third and the collector of the fourth bipolar transistor; and
where the base of the fourth bipolar transistor is connected to a node located between the emitter of the sixth bipolar transistor and the corresponding current source, and the base of the sixth bipolar transistor is connected to a node located between the emitter of the first and the collector of the second bipolar transistor.
The sensitivity of the current limiting circuit according to the invention is increased in this embodiment.
In accordance with another feature of the invention, the current sources of the fifth and sixth bipolar transistors are a resistor in each case.
In accordance with a further feature of the invention, the current sources of the fifth and sixth bipolar transistors are an NMOS transistor in each case.
In accordance with a concomitant feature of the invention, the common gate potential of the NMOS transistors is the potential of the common base terminal of the first and third bipolar transistors.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a current limiting circuit, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.